Courtesy Meade
Courtesy Meade
If the information you dig up leaves you feeling more confused, think about joining a local astronomy club. Some are free, others have a low annual membership fee.
First, get familiar with the sky. Can you find the Andromeda galaxy? What kinds of nebulas are there in the different constellations? It is best to buy a book that includes descriptions and star charts for the beginner. Also, subscribe to a popular astronomy magazine. Most of them are aimed directly at the back yard observer.
If you have already planned on buying a telescope from a department store because the price can't be beat make sure you take a list of what to avoid.
When discussing focal ratio it is also necessary to discuss magnification. Contrary to popular belief magnification is the least important factor in purchasing a telescope. The reason is because the more you magnify an object the dimmer and more blurry it becomes.
If you have superb optics on your telescope the greatest useful magnification you will get is about 40-50 times per inch of aperture. But, in reality you probably will get nowhere near that much magnification with a good image because of bad seeing which is a disturbance caused by hot and cold air meeting in the atmosphere that will make your image blur and deform at high power.
The last thing to look for in a telescope is the finderscope. Some telescopes won't even come with a finder but that is alright because you can purchase a finder for about $50.00. The two most common types of finders are refractor finders and reflex sights.
There are three main types of telescopes on the market today: refractors, Newtonian reflectors, and catadrioptics. All three are highly efficient systems but they all have their pros and cons.
These are the most commonly seen telescopes. Refractors work by using an objective lens to bend light. If the optics are good this results in a very sharp picture with high contrast. The three types of refractors are non-achromatic, achromatic, and apochromatic.
These telescopes give you the most aperture for the dollar. A Newtonian reflector uses mirrors to reflect and focus light on a converged point. Newtonian reflectors give very sharp views with almost as much contrast as an achromatic reflector. These telescopes are good for any astronomical use you may have for them. A reflector is the most cost effective telescope you can buy.
This is the last type of telescope There are two types of catadrioptics: The Schmitt Cassegrain and the Maksutov.
Do a little research first. The internet provides an easy access to information of all kinds. Just keep in mind not all of the information accessed on the web is precise or honest. Check a few of the astronomy magazines on-line.
Don't forget to stop in at the places who make the telescopes!
One big rule you will hear everywhere, NEVER buy from a department store. Most of them are not bent on selling quality telescopes. The prices are fantastic if the only thing you want to look at are the craters of the Moon. If you would like to observe other things in the night sky as well, avoid department stores at all costs.
The most important factor in buying a telescope is aperture. Aperture is the size of the objective lens on a refractor and the size of the primary mirror on a reflector or catadrioptic. The more aperture a telescope has the more light it can gather and th e higher a magnification it can use. Light gathering is extremely important in a telescope, if you plan to use it for deep-sky observing.
This is the focal length, (The length from the objective lens or the primary mirror to the focus), divided by the aperture of the telescope. A low focal ratio like 4.5 or 6 yields a wide image with a loss in contrast which is best for deep-sky ob serving. A high focal ratio like 9 or 15 has a narrower field of view than a low focal ratio but it has better contrast and it holds high magnification better. Thus, it is well suited for planetary, solar or lunar observing.
Dobsonian mounts are mounts for Newtonian reflectors that are altazimuth in design. They are extremely stable because they are very low to the ground and they are made of wood. They have
bearings made of nylon or teflon which allows it to move in altitu de or azimuth very smoothly. The greatest quality of the Dobsonian mount is that it is very inexpensive, works well and it can even be made easily at home.
These are used mostly on refractors. They work like the Dobsonian mount but they are much less stable. They are on top of a tripod which reduces their stability. These mounts are usually used on cheap department store refractors and they should be avoided because the only good mounts of this design will cost you more than $500.00.
Telescopes usually come with eyepieces. They have three different size barrel diameters .965",1.25"and 2". The wider the barrel the better. This is because there is not an adequate .965" eyepiece in the world. Do not buy any telescope that has this size eyepiece because it is a sure sign that telescope will be a lemon. 1.25" eyepieces are the standard size in the industry and they usually are very sharp and have a wide field of view. Kellner and Plossl's are examples of good 1.25" eyepieces. 2" eyepieces are rather uncommon on telescopes that cost less than $500.00 but they offer incredible wide fields and they only come with top-notch telescopes.
Refractor finders have crosshairs in them to help zero in on objects. These types of finders work very well. A refractor finder is also very easy to install because it only takes 2 screws to install it. Sometimes it's a pain in the neck, but once you get the hang of it, you'll wonder what you ever did without it. Just set up the center of the cross hairs on the object you want to look at and it is right there in the view of the scope. The only drawback is that it makes the image upside-down.
These finders are supposed to be superb for finding objects you can see with the naked eye like the moon, planets and bright deep-space objects. They have a flat piece of glass that has a L.E.D. shined on it that makes a bullseye. The only thing the observer has to do is line the bullseye up with the object he/she wants to see and it will be in the telescopes field of view. If you don't like looking at objects upside-down then this is probably the finder scope for you.
They use one or two convex lenses to focus light. They have severe chromatic aberration because they do not focus all colors of light in the same spot which gives them terrible views. These are your typical department store refractors. They are very cheap in price but they are almost useless for astronomy. Non-achromatic refractors are best avoided.
They use a concave and a convex lens to bend light. This ensures that most colors of light focus at the same point. These telescopes have sharp views and good contrast but, they are very expensive for their aperture. For $500.00 the largest refractor you could get would be about three inches which would be an O.K. plantary viewing telescope but it would be almost useless for deep-space viewing. Also, these telescopes tend to give you blue halos around the stars.
They use two lenses shaped like an achromatic refractors except they are made of two different types of glass which allows them to focus all colors of light at the same spot. These telescopes give without a doubt, the sharpest views and the highest contrast. They have a big drawback though, there is not a single telescope of this design that I know of that can be bought new for under $500.00, but if you can find a used one and your interests are only planetary viewing buy one of these.
It combines a refractor and a reflector in one package. The resulting telescope is extremely portable, compact and user friendly. There is a drawback to these telescopes though; they are very expensive and they have less contrast than other types of telescopes except the non-achromatic refractor. If you find one that is used and it costs less than $500.00 it will be a
good choice if compactness, portability and user friendliness are your prime consideration.
Telescopes of this design are basically the same as Schmitt Cassegrains except their corrector plate is curved which allows greater contrast and a flatter field. If you can find a used Maksutov with a 6" aperture or greater, in good working order and for less than $500.00 buy it before it is gone because it will be the deal of the century.
I hope you have found this page useful. If I have left anything out, posted wrong information, or you think there are other things that should be added please let me know.
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